U.S. patent application number 12/094110 was filed with the patent office on 2009-06-25 for carbon fibrous structure.
This patent application is currently assigned to BUSSAN NANOTECH RESEARCH INSTITUTE INC.. Invention is credited to Fuminori Munekane, Kazuhiro Osato, Jiayi Shan, Takayuki Tsukada.
Application Number | 20090162636 12/094110 |
Document ID | / |
Family ID | 38048680 |
Filed Date | 2009-06-25 |
United States Patent
Application |
20090162636 |
Kind Code |
A1 |
Shan; Jiayi ; et
al. |
June 25, 2009 |
CARBON FIBROUS STRUCTURE
Abstract
Disclosed is a carbon fibrous structure which comprises a
granular part and 2-20 pieces of carbon fibers each of which has an
outside diameter of 15-100 nm and which are extend outwardly from
the granular part, wherein the granular part is produced in a
growth process of the carbon fibers, wherein the size of granular
part is 1.3 or more of times larger than the outside diameter of
the carbon fibers, and wherein the mean length of the carbon fibers
is not more than 20 .mu.m. The carbon fibrous structure improves
the physical properties of the matrix, such as electric,
mechanical, or thermal properties, while maintaining the other
properties of the matrix, even when added at a small amount.
Inventors: |
Shan; Jiayi; (Tokyo, JP)
; Munekane; Fuminori; (Tokyo, JP) ; Tsukada;
Takayuki; (Tokyo, JP) ; Osato; Kazuhiro;
(Tokyo, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
BUSSAN NANOTECH RESEARCH INSTITUTE
INC.
Tokyo
JP
MITSUI & CO., LTD.
Tokyo
JP
|
Family ID: |
38048680 |
Appl. No.: |
12/094110 |
Filed: |
November 17, 2006 |
PCT Filed: |
November 17, 2006 |
PCT NO: |
PCT/JP2006/322970 |
371 Date: |
May 16, 2008 |
Current U.S.
Class: |
428/323 |
Current CPC
Class: |
Y10T 428/30 20150115;
B82Y 30/00 20130101; D01F 9/127 20130101; Y10T 428/2924 20150115;
Y10T 428/2927 20150115; Y10T 428/298 20150115; Y10T 428/25
20150115; Y10T 428/2925 20150115 |
Class at
Publication: |
428/323 |
International
Class: |
B32B 5/16 20060101
B32B005/16 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2005 |
JP |
2005-334887 |
Claims
1. Carbon fibrous structure which comprises a granular part and
2-20 pieces of carbon fibers each of which has an outside diameter
of 15-100 nm and which are extend outwardly from the granular part,
wherein the granular part is produced in a growth process of the
carbon fibers, wherein the size of granular part is 1.3 or more of
times larger than the outside diameter of the carbon fibers, and
wherein the mean length of the carbon fibers is not more than 20
.mu.m.
2. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure which has a bulk density of 0.0001-0.05
g/cm.sup.3.
3. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure has an I.sub.D/I.sub.G ratio of not more
than 0.2, and an I.sub.G'/I.sub.G ratio of 0.6-1.2, which are
determined by Raman spectroscopy.
4. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure has a combustion initiation temperature in
air of not less than 700.degree. C.
5. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure is produced using as carbon sources at
least two carbon compounds which have different decomposition
temperatures.
6. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure is produced by creating a turbulent flow
in a catalyst included raw material gas in a temperature range of
400-1000.degree. C.
7. The carbon fibrous structure according to claim 1, wherein the
carbon fibrous structure is obtained by using as a precursor a
carbon fibrous structure which comprises a three dimensional
network of carbon fibers each having an outside diameter of 15-100
nm, and cutting the carbon fibers of the precursor at defect
portions of the carbon fibers.
Description
TECHNICAL FIELD
[0001] This invention relates to fine carbon fibrous structures,
particularly, structures that are composed of fine carbon fibers
wherein each of the fibers is composed of tubular laminates of fine
carbon sheets and which are extended outwardly from a central
granular part. The fibrous structures are suitable as additives to
be added to solid materials, such as resin, ceramics, metal, etc.,
to improve physical properties, such as electric, mechanical, or
thermal properties, of the solid materials, and also as additives
to be added to liquid materials, such as fuels, lubricant oils, and
etc., to improve physical properties, such as thermal property, of
the liquid materials.
BACKGROUND ART
[0002] To date, carbon fibers have been used in various composite
materials because of their good mechanical properties and high
electric conductivity.
[0003] Recently, higher functionalities have come to be required
for various materials. Additives which can improve physical
properties, such as electric, mechanical, or thermal properties, of
a matrix comprised of solid materials, such as resin, ceramics, and
metal, without damaging the characteristics of the matrix have been
sought after. Additionally, additives which can improve physical
properties of liquids, such as fuels, oil, and lubricants have also
been sought.
[0004] Incidentally, fine carbon fibers, such as carbon nano
structures exemplified by the carbon nanotube (hereinafter,
referred to also as "CNT"), have been attracting public attention
in various fields.
[0005] The graphite layers that make up the carbon nano structures
are materials normally comprised of regular arrays of six-membered
rings whose structures can bring about specific electrical
properties, as well as chemically, mechanically, and thermally
stable properties. As long as such fine carbon fibers can retain
such properties upon combining and dispersing into solid materials,
including various resins, ceramics, metals, etc., or into liquid
materials, including fuels, lubricant agents, etc., their
usefulness as additives for improving material properties can be
expected.
[0006] On the other hand, however, such fine carbon fibers
unfortunately show an aggregate state even just after their
synthesis. When these aggregates are used as-is, the fine carbon
fibers would be poorly dispersed, and thus the product obtained
would not benefit from the desirable properties of the nano
structures. Accordingly, given a desired property such as electric
conductivity for a matrix such as resin, it is necessary that the
fine carbon fibers would be added in a large amount.
[0007] Patent Literature 1 discloses a resin composition comprising
aggregates wherein each of the aggregate is composed of mutually
entangled carbon fibrils having 3.5-70 nm in diameter, and wherein
the aggregates possess a diameter in the range of 0.10 to 0.25 mm
with a maximum diameter of not more than 0.25 mm. It is noted that
the numeric data such as the maximum diameter, diameter, etc., for
the carbon fibril aggregates are those measured prior to combining
with a resin, as is clear from the descriptions in the examples and
other parts of the Patent Literature 1. Patent Literature 2
discloses a composite material where a carbon fibrous material is
added to the matrix, the carbon fibrous material mainly comprising
aggregates each of which is composed of carbon fibers having
50-5000 nm in diameter, the mutual contacting points among the
carbon fibers being fixed with carbonized carbonaceous substance,
and each aggregates having a size of 5 .mu.m-500 .mu.m. In the
Patent Literature 2, the numeric data such as the size of
aggregate, etc., are those measured prior to the combining into
resin, too.
[0008] Using carbon fiber aggregates such as described above, it is
expected that the dispersibility of carbon nano structures within a
resin matrix will improve to a certain degree as compared to that
of using bigger lumps of carbon fibers. The aggregates prepared by
dispersing carbon fibrils under a certain shearing force, such as
in a vibrating ball mill or the like according to the Patent
Literature 1, however, have relatively high bulk densities. Thus,
they do not fulfill the need for ideal additives that is capable of
improving various characteristics, such as electric conductivity,
of a matrix effectively at minuscule dosages.
[0009] With respect to the carbon fibrous structure disclosed in
the Patent Literature 2, it is necessary to provide an additional
step for fixing carbon fibers at their mutual contacting points
after synthesis of the carbon fibers, and thus the efficiency of
manufacturing becomes worse. Further, since the carbon fibrous
structure is manufactured by heating carbon fibers in a state such
that mutual contacting points among the carbon fibers are formed by
compression molding after synthesis of the carbon fibers, and
wherein fixing of fibers at the contacting points is done by
carbonization of organic residues primarily attached to the surface
of the carbon fibers, or carbonization of an organic compound
additionally added as a binder, the affixing forces at the
contacting points are weak. In addition, the electrical properties
of the carbon fibrous structures per se are not well, although a
certain degree of improvement in the electrical properties would be
expected as compared with the case of pulverized monofibrous carbon
fibers. Thus, when these carbon fibrous structures are added to a
matrix such as a resin, the carbon fibers fixed at the contacting
points are easily detached from each other, and the carbon fibrous
structures are no longer maintained in the matrix. Therefore, it is
not possible to construct preferable conductive paths in a matrix
such that good electrical properties may be conferred on the matrix
by a small additive amount of the fibrous structures. Furthermore,
when a binder is added to promote fixing and carbonization at the
contacting points, fibers in the obtained fibrous structures would
have large diameters and inferior surface characteristics because
the added binder is attached to the whole surface area of the
fibers rather than to a limited area on the contacting points.
Patent Literature 1: Japanese patent No. 2862578
Patent Literature 2: JP 2004-119386 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by this Invention
[0010] Therefore, this invention aims to provide carbon fibrous
structures which can improve the physical properties, such as
electric, mechanical, or thermal properties, of a matrix while
maintaining other properties of the matrix, when added to the
matrix at a sufficiently small amount.
Means for Solving the Problems
[0011] As a result of our diligent study for solving the above
problems, we, the inventors, have found that, in order to give
sufficient improvements in properties even in a small adding
amount, the effective things are to adapt carbon fibers having a
diameter as small as possible; to make an sparse structure of the
carbon fibers where the fibers are mutually combined tightly so
that the fibers do not behave individually and which sustains their
sparse state in the fluorine resin; and to adapt as the carbon
fibers per se ones which are designed to have a minimum amount of
defects, and finally, we have accomplished the present
invention.
[0012] The present invention for solving the above mentioned
problems is, therefore, a carbon fibrous structure which comprises
a granular part and 2-20 pieces of carbon fibers each of which has
an outside diameter of 15-100 nm and which are extend outwardly
from the granular part, wherein the granular part is produced in a
growth process of the carbon fibers, wherein the size of granular
part is 1.3 or more of times larger than the outside diameter of
the carbon fibers, and wherein the mean length of the carbon fibers
is not more than 20 .mu.m.
[0013] The present invention also provides the above mentioned
carbon fibrous structure which has a bulk density of 0.0001-0.05
g/cm.sup.3
[0014] Further, the present invention provides the above mentioned
carbon fibrous structure which has an I.sub.D/I.sub.G ratio of not
more than 0.2, and an I.sub.G'/I.sub.G ratio of 0.6-1.2, which are
determined by Raman spectroscopy.
[0015] Furthermore, the present invention provides the above
mentioned carbon fibrous structure which has a combustion
initiation temperature in air of not less than 700.degree. C.
[0016] Still further, the present invention provides the above
mentioned carbon fibrous structure which is produced using as
carbon sources of at least two carbon compounds, which have
different decomposition temperatures.
[0017] In addition, the present invention provides the above
mentioned carbon fibrous structure which is produced by creating a
turbulent flow in a catalyst included raw material gas in a
temperature range of 450-1000.degree. C.
[0018] Further, the present invention provides the above mentioned
carbon fibrous structure which is obtained by using as a precursor
a carbon fibrous structure which comprises a three dimensional
network of carbon fibers each having an outside diameter of 15-100
nm, and cutting the carbon fibers of the precursor at defect
portions of the carbon fibers.
EFFECTS OF THE INVENTION
[0019] According to the present invention, since the carbon fibrous
structures are comprised of carbon fibers which each has a
ultrathin diameter and which are bound together by a granular part
produced in a growth process of the carbon fibers so that the
concerned carbon fibers extend outwardly and three dimensionally
from the granular part, the carbon fibrous structures can disperse
promptly into a matrix such as a resin upon adding, while
maintaining their bulky structure. Even when they are added at a
small amount to a matrix, they can be distributed uniformly over
the matrix. Therefore, with respect to the electric properties, it
is possible to obtain good electric conductive paths throughout the
matrix even at a small dosage, and thus it is possible to improve
the electrical conductivity while maintaining a good transparency.
With respect to the mechanical and thermal properties, improvements
can be expected in analogous fashions, since the carbon fibrous
structures are distributed evenly as fillers over the matrix with
only a small dosage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1A is an optical micrograph of the carbon fibrous
structure according to the present invention.
[0021] FIG. 1B is another optical micrograph of the carbon fibrous
structure according to the present invention.
[0022] FIG. 1C is further another optical micrograph of the carbon
fibrous structure according to the present invention.
[0023] FIG. 2A is a TEM photo of the carbon fibrous structure
according to the present invention.
[0024] FIG. 2B is another TEM photo of the carbon fibrous structure
according to the present invention.
[0025] FIG. 2C is a further another TEM photo of the carbon fibrous
structure according to the present invention.
[0026] FIG. 2D is a still another TEM photo of the carbon fibrous
structure according to the present invention.
[0027] FIG. 3 is a SEM photo of a precursor.
[0028] FIG. 4 is another SEM photo of a precursor.
[0029] FIG. 5 is a TEM photo of a carbon fibrous structure
according to the present invention;
[0030] FIG. 6 is a schematic diagram illustrating a generation
furnace used for synthesis of the precursor in a Synthetic
Example.
[0031] FIG. 7 is an X-ray diffraction chart of the carbon fibrous
structure according to the present invention, the precursor for the
carbon fibrous structure, and a fibrous structure
(intermediate).
[0032] FIG. 8 is Raman spectra of a carbon fibrous structure
according to the present invention and the intermediate of the
carbon fibrous structure.
[0033] FIG. 9 is an optical micrograph of a composite material
where carbon fibrous structures according to the present invention
are used.
EXPLANATION OF NUMERALS
[0034] 1 Generation furnace [0035] 2 Inlet nozzle [0036] 3
Collision member [0037] 4 Raw material mixture gas supply port
[0038] a Inner diameter of inlet nozzle [0039] b Inner diameter of
generation furnace [0040] c Inner diameter of Collision member
[0041] d Distance from upper end of generation furnace to raw
material mixture gas supply port [0042] e Distance from raw
material mixture gas supply port to lower end of collision member
[0043] f Distance from raw material mixture gas supply port to
lower end of generation furnace
BEST MODE FOR CARRYING OUT THE INVENTION
[0044] Now, the present invention will be described in detail with
reference to some embodiments.
[0045] Carbon fibrous structure according to the present invention
is, as shown in optical micrographs of FIG. 1A, FIG. 1B and FIG.
1C, or TEM photos of FIG. 2A, FIG. 2B, and FIG. 2C, composed of
fine carbon fibers each having an outside diameter of 15-100 nm,
and a granular part at which the fine carbon fibers are tied
together so that the concerned carbon fibers are externally
elongated from the granular part. As the shape of the extended end
portions of the carbon fibers opposite to the end portions fixed
with the granular part, in addition to the round closed shapes
which are as-is shapes of the synthesized carbon fibers, some
opened shapes which are formed by cutting the innate end portions
of the synthesized carbon fibers off can be also observed, in TEM
photos of FIG. 2B, and FIG. 2C.
[0046] The reason for restricting the outside diameter of the
carbon fibers to a range of 15 nm to 100 nm is because when the
outside diameter is less than 15 nm, the cross-sections of the
carbon fibers do not have polygonal figures as described later.
According to physical properties, the smaller the diameter of a
fiber, the greater the number of carbon fibers will be for the same
weight. This property would be followed by an enhanced electric
conductivity. Thus, carbon fibrous structures having an outside
diameter exceeding 100 nm are not preferred for use as modifiers or
additives for a matrix such as a resin, etc. Particularly, it is
more desirable for the outside diameter of the carbon fibers to be
in the range of 20-70 nm. Carbon fibers that have a diameter within
the preferable range and whose tubular graphene sheets are layered
one by one in the direction that is orthogonal to the fiber axis,
i.e., being of a multilayer type, can enjoy a high flexural
rigidity and ample elasticity. In other words, such fibers would
have a property of being easy to restore their original shape after
undergoing any deformation. Therefore, these fibers tend to take a
sparse structure in the matrix, even if the carbon fibrous
structures have been compressed prior to being mixed into the
matrix material.
[0047] Annealing at a temperature of not less than 1800.degree. C.
causes the carbon fibers to have polygonal cross-sections.
Additionally, annealing lessens the spacing between the layered
graphene sheets and increases the true density of the carbon fiber
from 1.89 g/cm.sup.3 to 2.1 g/cm.sup.3. As a result, the carbon
fibers become denser and have fewer defects in both the stacking
direction and the surface direction of the graphene sheets that
make up the carbon fiber, and their flexural rigidity (EI) and
dispersibility in a resin can also be enhanced and improved.
[0048] Additionally, it is preferable that the outside diameter of
a fine carbon fiber undergoes a change along the axial direction of
the fiber. In the case that the outside diameter of the carbon
fiber is not constant, but changes along the length of the fiber,
it would be expected that some anchor effect may be provided to the
carbon fiber at the interface with the matrix material, and thus
migration of the carbon fibrous structure in the matrix can be
restrained, leading to improved dispersion stability.
[0049] Furthermore, with respect to the shapes of the end portions
of the fine carbon fibers, it is preferable that they include not
only the round closed shapes but also include the unrounded cut
shapes. When such opened cut shapes are existed, the friction
coefficient of the end portions can be increased because the
smoothness is deteriorated as compared with that on the round
closed shapes, and further, owing to the interaction between the
cut faces and matrix, the dispersion stability of the fibers is
enhanced.
[0050] With respect to the mean length of the fine carbon fibers
which constitutes the carbon fibrous structure, it is preferable to
be not more than 20 .mu.m. When the mean length is not more than 20
.mu.m, it is possible to avoid causing inferior dispersion of the
carbon fibrous structures into the matrix such as resin, wherein
the inferior dispersion is due to the mutual entanglements of the
fine carbon fibers. For instance, when the carbon fiber structures
according to the present invention are used as an additive agent to
a transparent matrix, the carbon fiber structures can provide
desired physical properties even in a small adding amount, because
they are likely to take sparse configuration and show a good
dispersibility. Thus, the matrix is hardly influenced by coloring
of black carbon fibers, and it is possible to produce products
having good transparency such as a transparent conductive film.
Incidentally, the mean length of the fine carbon fibers used herein
is determined by taking a picture of the carbon fibrous structures
with an electron microscope or the like, then tracing the
individual fine carbon fiber which are extended outwardly from the
granular part in the obtained image using an appropriate image
analysis software, e.g., WinRoof.TM. (trade name, marketed by
Mitani Corp.), thereby measuring the lengths of individual fine
carbon fibers, and then calculating the mean value.
[0051] Thus, in a carbon fibrous structure according to the present
invention, fine carbon fibers having a predetermined outside
diameter and a predetermined length configures the three
dimensional network and are bound together by a granular part
produced in a growth process of the carbon fibers so that the
carbon fibers are externally elongated from the granular part.
Since multiple fine carbon fibers are not only entangled with each
other, but fused together at the granular part, the carbon fibers
will not disperse as single fibers, but will be dispersed as bulky
carbon fibrous structures when added to a matrix such as a resin.
Further since the fine carbon fibers have a mutual relay point that
is the granular part and 2-20 pieces of fine carbon fibers,
preferably, 3-10 pieces of fine carbon fibers are extended
outwardly from the granular part, the carbon fiber structure can
act very advantageously on the formation of electrically conductive
paths as compared with the case of adding the corresponding fine
carbon fibers are added in their separated form to the matrix.
[0052] Since the granular part is produced in the growth process of
the carbon fibers, the carbon-carbon bonds in the granular part are
well developed. Further, the granular part appears to include mixed
state of sp.sup.2- and sp.sup.3-bonds, although it is not clear
accurately. After the synthesis process (in the "fibrous structure
(intermediate)", the granular part and the fibrous parts are
continuous mutually by virtue of a structure comprising patch-like
sheets of carbon atoms laminated together. Further, after the high
temperature treatment, at least a part of graphene layers
constituting the granular part is continued on graphene layers
constituting the fine carbon fibers elongated externally from the
granular part, as shown in FIG. 2D. In the carbon fibrous structure
according to the present invention, as symbolized by such a fact
that the graphene layers constituting the granular part is
continued on the graphene layers constituting the fine carbon
fibers, the granular part and the fine carbon fibers are linked
together (at least in a part) by carbon crystalline structural
bonds. Thus, strong couplings between the granular part and each
fine carbon fiber are produced.
[0053] With respect to the carbon fibers, the condition of being
"extended outwardly" from the granular part used herein means
principally that the carbon fibers and granular part are linked
together by carbon crystalline structural bonds as mentioned above,
but does not means that they are apparently combined together by
any additional binding agent (involving carbonaceous ones).
[0054] As traces of the fact that the granular part is produced in
the growth process of the carbon fibers as mentioned above, the
granular part has at least one catalyst particle or void therein,
the void being formed due to the volatilization and elimination of
the catalyst particle during the heating process after the
generation process. The void (or catalyst particle) is essentially
independent from hollow parts which are formed in individual fine
carbon fibers which are extended outwardly from the granular part
(although, a few voids which happened to be associated with the
hollow part may be observed).
[0055] Although the number of the catalyst particles or voids is
not particularly limited, it may be about 1-100 a granular
particle, more preferably, about 3-50 a granular particle. When the
granular part is formed under the presence of catalyst particles
the number of which is within the range mentioned above, the
granular part formed can have a desirable size as mentioned
later.
[0056] The per-unit size of the catalyst particle or void existing
in the granular particle may be, for example, 1-100 nm, preferably,
2-40 nm, and more preferably, 3-15 nm.
[0057] Furthermore, it is preferable that the diameter of the
granular part is larger than the outside diameter of the carbon
fibers as shown in FIG. 2A and FIG. 2B. Concretely, for example,
the diameter of granular part is 1.3-100 times larger than the
outside diameter of the carbon fibers, preferably 1.3-50 times, and
more preferably, 1.3-20 times larger, on average. When the granular
part, which is the binding site of the carbon fibers, has a much
larger particle diameter, that is, 1.3 times or more larger than
the outer diameter of the carbon fibers, the carbon fibers that are
externally elongated from the granular part have stronger binding
force, and thus, even when the carbon fibrous structures are
exposed to a relatively high shear stress during combining with a
matrix such as resin, they can be dispersed as maintaining its
three-dimensional carbon fibrous structures into the matrix. When
the granular part has an extremely larger particle diameter, that
is, exceeding 100 times of the outer diameter of the carbon fibers,
the undesirable possibility that the fibrous characteristics of the
carbon fibrous structure are lost will arise. Therefore, the carbon
fibrous structure will be not suitable for an additive or
compounding agent to various matrixes, and thus it is not
desirable. Particularly, the carbon fibrous structure will not
suitable for an additive of improving various physical properties
while maintaining the transmittance of the matrix. The "particle
diameter of the granular part" used herein is the value which is
measured by assuming that the granular part, which is the binding
site for the mutual carbon fibers, is one spherical particle.
[0058] Although the concrete value for the particle diameter of the
granular part will be depended on the size of the carbon fibrous
structure and the outer diameter of the fine carbon fiber in the
carbon fibrous structure, for example, it may be 20-500 nm, more
preferably, 20-400 nm, and most preferably, 20-300 nm, on average.
When the granular part is taken such a size of the particle
diameter, the granular part becomes one which is preferable to be a
base for 2-20 pieces of the extended fine carbon fibers.
[0059] Furthermore, the granular part may be roughly globular in
shape because the part is produced in the growth process of the
carbon fibers as mentioned above. On average, the degree of
roundness thereof may lay in the range of from 0.2 to <1,
preferably, 0.5 to 0.99, and more preferably, 0.7 to 0.98.
[0060] Additionally, the binding of the carbon fibers at the
granular part is very tight as compared with, for example, that in
the structure in which mutual contacting points among the carbon
fibers are fixed with carbonaceous material or carbonized substance
therefrom. It is also because the granular part is produced in the
growth process of the carbon fibers as mentioned above. Even under
such a condition as to bring about selective cutting at defect
portions of the carbon fibers of the carbon fibrous structure, the
granular part (the binding site) is maintained stably.
Specifically, for example, when the carbon fibrous structures are
dispersed in a liquid medium and then subjected to ultrasonic
treatment with a selected wavelength and a constant power under a
load condition by which the mean length of the carbon fibers is
reduced to be not more than 20 .mu.m as shown in the Examples
described later, the changing rate in the mean diameter of the
granular parts is not observed, thus, the granular parts, i.e., the
binding sites of fibers are maintained stably.
[0061] Furthermore, the carbon fibrous structure according to the
present invention may exhibit a bulky, loose form in which the
carbon fibers are sparsely dispersed, because the carbon fibrous
structure is comprised of carbon fibers which are bound together by
a central granular part so that the carbon fibers are externally
elongated from the granular part as mentioned above. Concretely, it
is desirable that the bulk density thereof is in the range of
0.0001-0.05 g/cm.sup.3. When the bulk density exceeds 0.05
g/cm.sup.3, the improvement of the physical properties in a matrix
such as a resin would become difficult with a small dosage.
[0062] Furthermore, a carbon fibrous structure according to the
present invention can enjoy good electric properties in itself,
since the carbon fibers in the structure are bound together by a
central granular part. For instance, it is desirable that a carbon
fibrous structure according to the present invention has a powder
electric resistance determined under a certain pressed density, 0.8
g/cm.sup.3, of not more than 0.06 .OMEGA.cm, more preferably, 0.001
to 0.05 .OMEGA.cm. If the particle's resistance exceeds 0.06
.OMEGA.cm, it may become difficult to obtain a good electrically
conductivity when the structure is added to a matrix such as a
resin.
[0063] In order to enhance the strength and electric conductivity
of a carbon fibrous structure according to the present invention,
it is desirable that the graphene sheets that make up the carbon
fibers have a small number of defects, and more specifically, for
example, the I.sub.D/I.sub.G ratio of the carbon fiber determined
by Raman spectroscopy is not more than 0.2, and the
I.sub.G'/I.sub.G ratio determined by the same is in the range of
0.6-1.2. Incidentally, in Raman spectroscopic analysis, with
respect to a large single crystal graphite, only the peak (G band)
at about 1580 cm.sup.-1 appears. When the crystals are of finite
ultrafine sizes or have any lattice defects, the peak (D band) at
about 1360 cm.sup.-1 can appear. Further when the range to be
measured is widened, a G' band which is a bilateral asymmetry peak
at about 2700 cm.sup.-1 can be observed. With respect to the carbon
fibrous structure according to the present invention, it is
preferable that the G' band observed shows a bilateral symmetry
shape as shown in FIG. 7. Although the derivation of the G' band is
not clear, it is considered that the G' band will take a bilateral
symmetry shape when the graphene sheet becomes a cylindrical shape.
Further, when the intensity of the D band is weak and the intensity
of the G' band is strong, it is considered that the graphene sheet
has a small amount of defects. Therefore, when both the intensity
ratio (R=I.sub.1360/I.sub.1580=I.sub.D/I.sub.G) of the D band and
the G band and the intensity ratio
(R.dbd.I.sub.2700/I.sub.1580=I.sub.G'/I.sub.G) of the G' band and
the G band are laid within the individual ranges as mentioned
above, it is possible to say that the number of defects in graphene
sheets is low.
[0064] Furthermore, it is desirable that the carbon fibrous
structure according to the present invention has a combustion
initiation temperature in air of not less than 700.degree. C. Such
a high thermal stability would be brought about by the above
mentioned facts that the graphene sheets has little defects and
that the carbon fibers have a predetermined outside diameter.
[0065] A carbon fibrous structure according to the present
invention having the above described, desirable configuration may
be prepared as follows, although it is not limited thereto.
[0066] Basically, an organic compound such as a hydrocarbon is
chemical thermally decomposed through the CVD process in the
presence of ultrafine particles of a transition metal as a catalyst
in order to obtain a fibrous structure (intermediate), and then the
intermediate thus obtained undergoes a high temperature heating
treatment in order to obtain carbon fiber precursor, and thereafter
the precursor undergoes process of cutting selectively.
[0067] As a raw material organic compound, hydrocarbons such as
benzene, toluene, xylene; carbon monoxide (CO); and alcohols such
as ethanol may be used. It is preferable, but not limited, to use
as carbon sources at least two carbon compounds which have
different decomposition temperatures. Incidentally, the words "at
least two carbon compounds" used herein not only include two or
more kinds of raw materials, but also include one kind of raw
material that can undergo a reaction, such as hydrodealkylation of
toluene or xylene, during the course of synthesis of the fibrous
structure such that in the subsequent thermal decomposition
procedure it can function as at least two kinds of carbon compounds
having different decomposition temperatures.
[0068] When as the carbon sources at least two kinds of carbon
compounds are provided in the thermal decomposition reaction
system, the decomposition temperatures of individual carbon
compounds may be varied not only by the kinds of the carbon
compounds, but also by the gas partial pressures of individual
carbon compounds, or molar ratio between the compounds. Therefore,
as the carbon compounds, a relatively large number of combinations
can be used by adjusting the composition ratio of two or more
carbon compounds in the raw gas.
[0069] For example, the fibrous structure (intermediate) can be
prepared by using two or more carbon compounds in combination,
while adjusting the gas partial pressures of the carbon compounds
so that each compound performs mutually different decomposition
temperature within a selected thermal decomposition reaction
temperature range, and/or adjusting the residence time for the
carbon compounds in the selected temperature region, wherein the
carbon compounds to be selected are selected from the group
consisting of alkanes or cycloalkanes such as methane, ethane,
propanes, butanes, pentanes, hexanes, heptanes, cyclopropane,
cycrohexane, particularly, alkanes having 1-7 carbon atoms; alkenes
or cycloolefin such as ethylene, propylene, butylenes, pentenes,
heptenes, cyclopentene, particularly, alkenes having 1-7 carbon
atoms; alkynes such as acetylene, propyne, particularly, alkynes
having 1-7 carbon atoms; aromatic or heteroaromatic hydrorocarbons
such as benzene, toluene, styrene, xylene, naphthalene, methyl
naphtalene, indene, phenanthrene, particularly, aromatic or
heteroaromatic hydrorocarbons having 6-18 carbon atoms; alcohols
such as methanol, ethanol, particularly, alcohols having 1-7 carbon
atoms; and other carbon compounds involving such as carbon
monoxide, ketones, ethers. Further, to optimize the mixing ratio
can contribute to the efficiency of the preparation.
[0070] When a combination of methane and benzene is utilized among
such combinations of two or more carbon compounds, it is desirable
that the molar ratio of methane/benzene is >1-600, preferably,
1.1-200, and more preferably 3-100. The ratio is for the gas
composition ratio at the inlet of the reaction furnace. For
instance, when as one of carbon sources toluene is used, in
consideration of the matter that 100% of the toluene decomposes
into methane and benzene in proportions of 1:1 in the reaction
furnace, only a deficiency of methane may be supplied separately.
For example, in the case of adjusting the methane/benzene molar
ratio to 3, 2 mol methane may be added to 1 mol toluene. As the
methane to be added to the toluene, it is possible to use the
methane which is contained as an unreacted form in the exhaust gas
discharged from the reaction furnace, as well as a fresh methane
specially supplied.
[0071] Using the composition ratio within such a range, it is
possible to obtain the fibrous structure (intermediate) of three
dimensional network structure in which both the carbon fiber parts
and granular parts are efficiently developed.
[0072] Inert gases such as argon, helium, xenon; and hydrogen may
be used as an atmosphere gas.
[0073] A mixture of transition metal such as iron, cobalt,
molybdenum, or transition metal compounds such as ferrocene, metal
acetate; and sulfur or a sulfur compound such as thiophene, ferric
sulfide; may be used as a catalyst.
[0074] The fibrous structure (intermediate) may be synthesized
using a CVD process with hydrocarbon or etc., which has been
conventionally used in the art. The steps may comprise gasifying a
mixture of hydrocarbon and a catalyst as a raw material, supplying
the gasified mixture into a reaction furnace along with a carrier
gas such as hydrogen gas, etc., and undergoing thermal
decomposition at a temperature in the range of 800.degree.
C.-1300.degree. C. By following such synthesis procedures, the
product obtained is an aggregate, which is of several to several
tens of centimeters in size and which is composed of plural fibrous
structures (intermediates), each of which has a three dimensional
configuration where fibers having 15-100 nm in outside diameter are
bound together by a granular part that has grown around the
catalyst particle as the nucleus.
[0075] The thermal decomposition reaction of the hydrocarbon raw
material mainly occurs on the surface of the catalyst particles or
on growing surface of granular parts that have grown around the
catalyst particles as the nucleus, and the fibrous growth of carbon
may be achieved when the recrystallization of the carbons generated
by the decomposition progresses in a constant direction. When
obtaining carbon fibrous structures according to the present
invention, however, the balance between the thermal decomposition
rate and the carbon fiber growth rate is intentionally varied.
Namely, for instance, as mentioned above, to use as carbon sources
at least two kinds of carbon compounds having different
decomposition temperatures may allow the carbonaceous material to
grow three dimensionally around the granular part as a centre,
rather than in one dimensional direction. The three dimensional
growth of the carbon fibers depends not only on the balance between
the thermal decomposition rate and the growing rate, but also on
the selectivity of the crystal face of the catalyst particle,
residence time in the reaction furnace, temperature distribution in
the furnace, etc. The balance between the decomposition rate and
the growing rate is affected not only by the kinds of carbon
sources mentioned above, but also by reaction temperatures, and gas
temperatures, etc. Generally, when the growing rate is faster than
the decomposition rate, the carbon material tends to grow into
fibers, whereas when the thermal decomposition rate is faster than
the growing rate, the carbon material tends to grow in peripheral
directions of the catalyst particle. Accordingly, by changing the
balance between the thermal decomposition rate and the growing rate
intentionally, it is possible to control the growth of carbon
material to occur in multi-direction rather than in single
direction, and to produce the three dimensional structures.
[0076] In order to form the above mentioned three-dimensional
configuration in the produced fibrous structure (intermediate),
where the fibers are bound together by a granular part, with ease,
it is desirable to optimize the compositions such as the catalyst
used, the residence time in the reaction furnace, the reaction
temperature and the gas temperature.
[0077] With respect to the method for preparing the fibrous
structure (intermediate) with efficiency, as another approach to
the aforementioned one that two or more carbon compounds which have
mutually different decomposition temperature are used in an
appropriate mixing ratio, there is an approach that the raw
material gas supplied into the reaction furnace from a supply port
is forced to form a turbulent flow in proximity to the supply port.
The "turbulent flow" used herein means a furiously irregular flow,
such as flow with vortexes.
[0078] In the reaction furnace, immediately after the raw material
gas is supplied into the reaction furnace from the supply port,
metal catalyst fine particles are produced by the decomposition of
the transition metal compound as the catalyst involved in the raw
material gas. The production of the fine particles is carried out
through the following steps. Namely, at first, the transition metal
compound is decomposed to make metal atoms, then, plural number of,
for example, about one hundred of metal atoms come into collisions
with each other to create a cluster. At the created cluster state,
it can not function as a catalyst for the fibrous structure
(intermediate). Then, the clusters are further aggregated by
collisions with each other to grow into a metal crystalline
particle of about 3-10 nm in size, and which particle comes into
use as the metal catalyst fine particle for producing the fibrous
structure (intermediate).
[0079] During the catalyst formation process as mentioned above, if
the vortex flows belonging to the furiously turbulent flow are
present, it is possible that the collisions of carbon atoms or
collisions of clusters become more vigorously as compared with the
collisions only due to the Brownian movement of atoms or
collisions, and thus the collision frequency per unit time is
enhanced so that the metal catalyst fine particles are produced
within a shorter time and with higher efficiency. Further, since
concentration, temperature, and etc. are homogenized by the force
of vortex flow, the obtained metal catalyst fine particles become
uniform in size.
[0080] Additionally, during the process of producing metal catalyst
fine particles, a metal catalyst particles' aggregate in which
numerous metal crystalline particles was aggregated by vigorous
collisions with the force of vortex flows can be also formed. Since
the metal catalyst particles are rapidly produced as mentioned
above and thus the surface area of the metal catalyst as the site
for the decomposition reaction of the carbon compound becomes
large, the decomposition of carbon compound can be accelerated so
that an ample amount of carbonaceous material can be provided.
Whereby, the fine carbon fibers grow up in a radial pattern by
taking individual metal catalyst particles in the aggregate as
nuclei. When the thermal decomposition rate of a part of carbon
compounds is faster than the growing rate of the carbon material as
previously described, the carbon material may also grow in the
circumferential direction so as to form the granular part around
the aggregate, and thus the fibrous structure (intermediate) of the
desired three dimensional configuration may be obtained with
efficiency.
[0081] Incidentally, it may be also considered that there is a
possibility that some of the metal catalyst fine particles in the
aggregate are ones that have a lower activity than the other
particles or ones that are deactivated on the reaction. If
non-fibrous or very short fibrous carbon material layers grown by
such catalyst fine particles before or after the catalyst fine
particles aggregate are present at the circumferential area of the
aggregate, the granular part of the intermediate may be formed.
[0082] The concrete means for creating the turbulence to the raw
material gas flow near the supply port for the raw material gas,
especially in the temperature range of 450-1000.degree. C. which
would be deduced as the range for creation and formation of the
metal catalyst particles from the reaction kinetics, is not
particularly limited. For example, it is adaptable to provide some
type of collision member at a position where the raw material gas
flow introduced from the supply port can be interfered by the
collision section. The shape of the collision section is not
particularly limited, as far as an adequate turbulent flow can be
formed in the reaction furnace by the vortex flow which is created
at the collision section as the starting point. For example,
embodiments where various shapes of baffles, paddles, tapered
tubes, umbrella shaped elements, and etc., are used singly or in
varying combinations and located at one or more positions may be
adaptable.
[0083] The fibrous structure (intermediate), obtained by heating
the mixture of the catalyst and hydrocarbon at a constant
temperature in the range of 800.degree. C.-1300.degree. C. after
the creation and formation of the metal catalyst particle at a
temperature of 450.degree. C.-1000.degree. C., has a structure that
resembles sheets of carbon atoms laminated together, (and being
still in half-raw, or incomplete condition). When analyzed with
Raman spectroscopy, the D band of the intermediate is very large
and many defects are observed. Further, the obtained fibrous
structure (intermediate) is associated with unreacted raw
materials, nonfibrous carbon, tar moiety, and catalyst metal.
[0084] Therefore, the fibrous structure (intermediate) is subjected
to a high temperature heat treatment of 1800-2800.degree. C. using
a proper method in order to remove such residues from the
intermediate and to produce the intended precursor which has few
defects at the granular part and has an appropriate numbers of
defects at the carbon fiber part.
[0085] For instance, the fibrous structure (intermediate) may be
heated at 800-1300.degree. C. to remove the unreacted raw material
and volatile flux such as the tar moiety, and thereafter annealed
at a high temperature of 1800-2800.degree. C. to produce the
intended precursor and, concurrently, to vaporize the catalyst
metal, which is included in the fibers, to remove it from the
fibers. In this process, it is possible to add a small amount of a
reducing gas and carbon monoxide into the inert gas atmosphere to
protect the carbon structures.
[0086] By annealing the fibrous structure (intermediate) at a
temperature of 1800-2800.degree. C., the patch-like sheets of
carbon atoms are rearranged to associate mutually and then form
multiple graphene sheet-like layers. When the annealing temperature
is not more than 1800.degree. C., the obtained precursor has a
large numbers of defect portions, and thus there is a fear that the
desired physical properties such as electrical conductivity are not
attained. On the other hand, when the intermediate undergoes heat
treatment at a temperature of more than 2800.degree. C., the fine
carbon fibers become particularly denser and come to have an
extremely small number of defect parts, and the strength of the
fine carbon fiber parts becomes relatively higher as compared with
that of the granular part. Therefore, there is a fear that the
selective cutting at the defect portions of the fine carbon fiber
parts mentioned later becomes difficult. As mentioned above, with
respect to the precursor which is prepared by annealing of the
fibrous structure (intermediate), although it is preferable that
the number of the defects in the graphene sheets which constitute
the fine carbon fibers is low, but the defects should exist to a
certain proper extent in order to cut the fibers. Thus, it is
preferable to prepare the precursor by annealing the fibrous
structure (intermediate) at a temperature in the range of
1800-2800.degree. C.
[0087] Further, it is preferable that the precursor has an
area-based circle-equivalent mean diameter of 50-100 .mu.m, and
more preferably, 60-90 .mu.m. The "area-based circle-equivalent
mean diameter" used herein is the value which is determined by
taking a picture of the outside shapes of the precursors with a
suitable electron microscope, etc., tracing the contours of the
respective precursors in the obtained picture using a suitable
image analysis software, e.g., WinRoof.TM. (Mitani Corp.), and
measuring the area within each individual contour, calculating the
circle-equivalent mean diameter of each individual precursors, and
then, averaging the calculated data.
[0088] Incidentally, in order to obtain the desirable carbon
fibrous structure, it is preferable to perform a crushing treatment
before or after such a high temperature heat treatment, in order to
obtain the precursors each having an area-based circle-equivalent
mean diameter of several micrometers to several tens micrometers,
from the viewpoint of handling.
[0089] with respect to the precursor which is prepared by annealing
of the fibrous structure (intermediate), although it is preferable
that the number of the defects in the graphene sheets which
constitute the fine carbon fibers at the stage of the precursor is
low from the viewpoint of giving a high strength and a high
electrical conductivity to the carbon fibrous structure of the
present invention as the final product, but the defects should
exist to a certain proper extent in order to cut the fibers.
Concretely, for instance, it is preferable that the I.sub.D/I.sub.G
ratio of the precursor determined by Raman spectroscopy is not more
than 0.2, and the I.sub.G'/I.sub.G ratio determined by the same is
in the range of 0.6-1.2. Further, it is preferable that the G' band
of the precursor shows a almost bilateral symmetry shape. Although
the derivation of the G' band is not clear, it is considered that
the G' band will take a bilateral symmetry shape when the graphene
sheet becomes a cylindrical shape. Further, when the intensity of
the D band is weak and the intensity of the G' band is strong, it
is considered that the graphene sheet has a small amount of
defects. Therefore, when both the intensity ratio
(R=I.sub.1360/I.sub.1580=I.sub.D/I.sub.G) of the D band and the G
band and the intensity ratio
(R.dbd.I.sub.2700/I.sub.1580=I.sub.G'/I.sub.G) of the G' band and
the C band are laid within the individual ranges as mentioned
above, it is possible to say that the number of defects in graphene
sheets is low, but the defects exist to a certain extent suitable
for performing the selective cutting the carbon fiber parts at the
defect portions.
[0090] Incidentally, the "defect" described herein denotes the
incomplete portion of atomic arrangement of the graphene sheet
(lattice defect) which is caused by the entry of unnecessary atom
as an impurity, the lack of necessary carbon atom, or the
misalignment of the carbon atom, etc.
[0091] In the arrangement of the graphene sheet, the point defect
(invasion type, substitution type, defect due to hole (Frenkel
defect and Schottky defect)), the line defect (defect due to
dislocation (edge dislocation and screw dislocation), or the plane
defect (stacking fault) can appear. When these defects exist in the
precursor, it is possible to cut the fiber selectively at the
defect portion since the binding force between the carbon atoms at
such a defect portion is weak as compared with that at a portion
where the carbon atoms are regularly arranged in the graphene
sheet. As an example of such a defect portion, a TEM photo of a
defect portion which possesses a distorted and bent shape and which
exists in the fine carbon fiber is shown in FIG. 6.
[0092] In general, fine carbon fibers have a very large aspect
ratio, and they form a lump where they are densely entangled
mutually. Thus, the dispersibility of the fine carbon fibers in the
matrix becomes very worse. Therefore, if it is intended to provide
desired physical properties to the matrix, the addition of large
volume of the fine carbon fibers is required. Thus, it is difficult
to attain the improvement of the physical properties while
maintaining the good transmittance of the matrix.
[0093] We, the inventors, have found that a novel carbon fibrous
structure which excels in the dispersibility into the matrix, and
which has a granular parts and takes a three dimensional structure
of fine carbon fiber can be obtained by constructing a precursor of
a three dimensional structure which is provided with plural number
of fine carbon fibers each having defects to a certain extent and a
granular part by which the fine carbon fibers are bound together by
means of controlling the various conditions for the growth of the
fine carbon fibers, and cutting the fine carbon fibers in the
precursor selectively at the defect portions.
[0094] As the method for cutting the fine carbon fibers in the
precursor selectively at the defect portions, it is preferable that
the method does not cause any deterioration in the carbon fiber
parts of having no defect originally, that is, the method does not
create any fresh defect on the carbon fiber parts, although it is
not particularly limited thereto. For instance, it is possible to
cut selectively as follows.
[0095] A method where the precursors for the carbon fibrous
structures are dispersed in a liquid medium, and then the obtained
dispersion a ultrasonic waves are irradiated with ultrasonic waves
of a prescribed frequency at a constant power can be utilized. When
irradiating with the ultrasonic waves, standing waves corresponding
to the applied frequency are generated in the liquid medium, and
physical forces are produced every integral multiples of wavelength
.gamma./2, and thus it is possible to attain the selective cutting
of the carbon fibers at the defect portions where the bonding force
between the carbon atoms is weak.
[0096] For instance, in the case of utilizing the ultrasonic waves,
as the physical forces capable of performing such a selective
cutting of the carbon fiber can be divided roughly into two kinds.
One of them is the effect owing to the cavitation of low frequency
ultrasonic waves, and the other is the acceleration of the liquid
molecules in the liquid medium by high frequency ultrasonic waves
so as to allow the molecules to cut the carbon fibers
selectively.
[0097] Cavitation shows correlation with the dissolved gas(es) in
the liquid medium and the vapor pressure of the liquid medium. In
general, when an infinite number of the gas molecules existing in
the liquid medium are irradiated with the ultrasonic waves having a
frequency of 20-100 kHz, positive and negative pressures are
applied alternately to the gas molecules. Thus, the gas molecules
are compressed by the positive pressure, and the next moment the
compressed gas molecules expand extremely with the negative
pressure. By repeating the compression and the expansion
alternately, the gas molecules come to gain a very high pressure on
the compression, and at the compression limit the bubbles of gas
molecules burst and disappear. The shock waves created when the
bubbles burst act onto the defects in the fiber parts of the carbon
fibrous structure (intermediate), thereby the cavitation effect of
cutting the fiber is obtained.
[0098] As mentioned above, the carbon fibrous structure according
to the present invention can be obtained by cutting selectivity the
precursor which is composed of fine carbon fibers which are
allocated as three dimensional network structure, and a granular
part at which the fine carbon fibers are tied together so that the
concerned carbon fibers are externally elongated from the granular
part.
[0099] When two or more granular parts are present in a precursor,
wherein each granular part binds the fibers so as to form the three
dimensional network, the mean distance between adjacent granular
parts may be, for example, 0.5-100 .mu.m, preferably, 0.5-70 .mu.m,
and more preferably, 0.5-50 .mu.m. The distance between adjacent
granular parts used herein is determined by measuring distance from
the center of a granular part to the center of another granular
part which is adjacent the former granular part. When the mean
distance between the granular parts is less than 0.5 .mu.m, the
carbon fibrous structure which is obtained by subjecting the
precursor to the process of cutting selectively thereafter is
compelled to have a configuration where the carbon fibers are of
having a short length and they form an inadequately developed three
dimensional network. Therefore, it may become difficult to form
good electrically conductive paths when the carbon fiber structures
each having such an inadequately developed three dimensional
network are added and dispersed to the matrix. Meanwhile, when the
mean distance exceeds 100 .mu.m, many single carbon fibers which
are separated from each other are produced as a side product on the
process of cutting selectively, in addition to the intended carbon
fiber structures, and which is followed by a degression in the
yield of the carbon fibrous structures. Further, since the obtained
carbon fibrous structure comes to own relatively long carbon fiber,
and thus, an undesirable increase in viscosity may be expected to
happen upon adding and dispersing the carbon fibrous structures in
the matrix. The increase in viscosity may result in an inferior
dispersibility of the carbon fibrous structures to the matrix.
[0100] Therefore, the mean length of the carbon fibers which are
extended from the granular part in the carbon fiber structure
according to the present invention is preferable to be not more
than 20 .mu.m. Because the dispersibility is improved, the adding
amount to be needed can be reduced, and thus the carbon fibrous
structure according to the present invention can be utilized for
the purpose of showing good transparency such as transparent
electrically conductive film.
[0101] Furthermore, in order to give a high strength and a good
electrical conductivity, it is preferable that the I.sub.D/I.sub.G
ratio of the carbon fibrous structure of the present invention is
not more than 0.2, and the I.sub.G'/I.sub.G ratio is in the range
of 0.6-1.2, wherein the ratios are determined by Raman
spectroscopy.
[0102] Incidentally, when the carbon fibrous structures are added
as additive to a matrix, the carbon fibrous structures may be used
solely as the additive. Alternatively, it is also possible to use
the single fine carbon fibers having no granular part and/or the
precursors each having the three dimensional network structure as
other additives, along with the carbon fibrous structure as a main
ingredient, in any combination and any mixing ratio. When using the
single fine carbon fibers having no granular part in combination
with the carbon fibrous structure, a certain cross linking effect
between them would be expected, and it is considered that the
effect may bring an advantage in the formation of the conductive
paths as compared with the case of using the single fine carbon
fibers solely.
[0103] The reason why the granular part (binding site) is sustained
stably is probably due to the fact that the metal catalyst minute
particles (including deactivated catalyst particles) exist in the
granular part intensively rather than the fine carbon fiber parts
at the state of the fibrous structure (intermediate). Incidentally,
on the observation using TEM, it is possible to confirm that most
of the metal catalyst minute particles exist in the granular part
of the fibrous structure (intermediate). These metal catalyst
minute particles would function as catalyst for regularly aligning
the graphite layer.
EXAMPLES
[0104] Hereinafter, this invention will be illustrated in detail by
practical examples. However, the invention is not limited to the
following examples.
[0105] The respective physical properties illustrated later are
measured by the following protocols.
<Area Based Circle-Equivalent Mean Diameter of Precursor>
[0106] First, a photograph of three dimensional network structures
(precursors) which are substance in the previous stage of the
carbon fibrous structures according to the present invention was
taken with SEM (200 magnifications). On the taken SEM photo,
contours of the individual carbon fibrous structures were traced
using the image analysis software, WinRoof.TM. (trade name,
marketed by Mitani Corp.), and area within each individual contour
was measured, circle-equivalent mean diameter of each individual
carbon fibrous structure was calculated, and then, the calculated
data were averaged to define the area based circle-equivalent mean
diameter of the precursors. On this determination, only precursors
with clear contours were taken as objects to be measured, and
broken ones with unclear contours were omitted. Using all
precursors that can be taken as objects in one single field of view
(approximately, 60-80 pieces), about 200 pieces in total were
measured with three fields of views.
<Mean Length of Fine Carbon Fibers in Precursor>
[0107] Photograph of precursors was taken with SEM (1000-3000
magnifications). On the taken SEM photo, all places where the
granular parts are mutually linked with a fine carbon fiber are
found out. Then, at the respective places, the distance between the
adjacent granular parts which are mutually linked with the fine
carbon fiber (the length of the fine carbon fiber including the
center of a granular part at one end to the center of another
granular part at another end) is measured using the image analysis
software, WinRoof.TM. (trade name, marketed by Mitani Corp.), and
then the data obtained are averaged in order to find out the mean
length. On this determination, only precursors with clear contours
were taken as objects to be measured, and broken ones with unclear
contours were omitted. Using all precursors that can be taken as
objects in one single field of view (approximately, 60-80 pieces),
about 200 pieces in total were measured with three fields of
views.
<Mean Length of Fine Carbon Fibers in Carbon Fibrous
Structure>
[0108] Photograph of carbon fibrous structures according to the
present invention was taken with SEM (1000-5000 magnifications). On
the taken SEM photo, the length of respective fine carbon fiber
from the center of the granular part to the opposite end portion of
the extended fine carbon fiber are measured using the image
analysis software, WinRoof.TM. (trade name, marketed by Mitani
Corp.), and then the data obtained are averaged in order to find
out the mean length. On this determination, only carbon fibrous
structures with clear contours were taken as objects to be
measured, and broken ones with unclear contours were omitted. Using
all carbon fibrous structures that can be taken as objects in one
single field of view (approximately, 60-80 pieces), about 200
pieces in total were measured with three fields of views.
<Mean Diameter and Roundness of the Granular Part, and Ratio of
the Granular Part to the Fine Carbon Fiber>
[0109] First, a photograph of the precursors or carbon fibrous
structures was taken with SEM.
[0110] On the SEM photo, assuming each individual granular part
which is the binding point of carbon fibers to be a particle,
contours of the individual granular parts were traced using the
image analysis software, WinRoof.TM. (trade name, marketed by
Mitani Corp.), and area within each individual contour was
measured, circle-equivalent mean diameter of each individual
granular part was calculated, and then, the calculated data were
averaged to determine the mean diameter of the granular parts of
the precursors or the carbon fibrous structures.
[0111] Roundness (R) is determined by inputting value of the area
(A) within each individual contour computed by the above and a
measured value of each individual contour's length (L) to the
following equation to calculate the roundness of each individual
granular part, and then, averaging the calculated data.
R=A*4.pi./L.sup.2 [Numerical Formula 1]
[0112] Further, the outer diameter of the fine carbon fibers in the
individual precursors or carbon fibrous structures to be measured
are determined, and then, from the outer diameter determined and
the circle-equivalent mean diameter of the granular part calculated
as above, the ratio of circle-equivalent mean diameter to the outer
diameter of the fine carbon fiber is calculated for each individual
precursor or the carbon fibrous structure, and then the data
obtained are averaged.
[0113] Incidentally, on the taken SEM photo, only precursors or
carbon fibrous structures with clear contours were taken as objects
to be measured, and broken ones with unclear contours were omitted.
Using all precursors or carbon fibrous structures that can be taken
as objects in one single field of view (approximately, 60-80
pieces), about 200 pieces of precursors or carbon fibrous
structures in total were measured with three fields of views.
<Measurement of Bulk Density>
[0114] 1 g of powder was placed into a 70 mm caliber transparent
cylinder equipped with a distribution plate, then air supply at 0.1
Mpa of pressure, and 1.3 liter in capacity was applied from the
lower side of the distribution plate in order to blow off the
powder and thereafter allowed the powder to settle naturally. After
the fifth air blowing, the height of the settled powder layer was
measured. Any 6 points were adopted as the measuring points, and
the average of the 6 points was calculated in order to determine
the bulk density.
<Raman Spectroscopic Analysis>
[0115] The Raman spectroscopic analysis was performed with LabRam
800 manufactured by HORIBA JOBIN YVON, S.A.S., using 514 nm argon
laser.
<TG Combustion Temperature>
[0116] Combustion behavior was determined using TG-DTA manufactured
by MAC SCIENCE CO. LTD., at air flow rate of 0.1 liter/minute and
heating rate of 10.degree. C./minute with respect to a sample of
the intermediate or the carbon fibrous structure which was weighed
to be 10 mg and placed in an alumina crucible.
[0117] When burning, TG indicates a quantity reduction and DTA
indicates an exothermic peak. Thus, the top position of the
exothermic peak was defined as the combustion initiation
temperature.
<X Ray Diffraction>
[0118] Using the powder X ray diffraction equipment (JDX3532,
manufactured by JEOL Ltd.), precursors after annealing processing
and carbon fibrous structures were determined. K.alpha. ray which
was generated with Cu tube at 40 kV, 30 mV was used, and the
measurement of the spacing was performed in accordance with the
method defined by The Japan Society for the Promotion of Science
(JSPS), described in "Latest Experimental Technique For Carbon
Materials (Analysis Part)", Edited by Carbon Society of Japan), and
as the internal standard silicon powder was used.
<Particle's Resistance and Decompressibility>
[0119] 1 g of powder sample was scaled, and then press-loaded into
a resinous die (inner dimensions: L 40 mm, W 10 mm, H 80 mm), and
the displacement and load were read out. A constant current was
applied to the powder by the four-terminal method, and in this
condition the voltage was measured. After measuring the voltage
until the density came to 0.9 g/cm.sup.3, the applied pressure was
released and the density after decompression was measured.
Measurements taken when the powder was compressed to 0.5, 0.8 or
0.9 g/cm.sup.3 were adopted as the particle's resistance.
<Total Light Transmittance>
[0120] Total light transmittance was determined in accordance with
JIS K 7361, by using a haze/transmittance meter (HM-150,
manufactured by MURAKAMI COLOR RESEARCH LABORATORY), for a coating
film having a prescribed thickness formed on a glass plate (total
light transmittance of 91.0%, 50.times.50.times.2 mm).
<Surface Resistivity>
[0121] 50.times.50 mm of coated harden film was prepared on a glass
plate. Using 4-pin probe type resistivity meters (MCP-T600,
MCP-HT4500, both manufactured by Mitsubishi Chemical), the
resistance (.OMEGA.) at nine points of the coated film surface was
measured, then the measured values are converted into those of
volume resistivity (.OMEGA.cm) by the resistivity meters, and then
average was calculated.
Synthetic Example 1
[0122] By the CVD process, carbon fibrous structures were
synthesized using toluene as the raw material.
[0123] The synthesis was carried out in the presence of a mixture
of ferrocene and thiophene as the catalyst, and under the reducing
atmosphere of hydrogen gas. Toluene and the catalyst were heated to
380.degree. C. along with the hydrogen gas, and then they were
supplied to the generation furnace, and underwent thermal
decomposition at 1250.degree. C. in order to obtain the fibrous
structures (intermediate).
[0124] The generation furnace used for the fibrous structures
(intermediate) is illustrated schematically in FIG. 6. As shown in
FIG. 6, the generation furnace 1 was equipped at the upper part
thereof with a inlet nozzle 2 for introducing the raw material
mixture gas comprising toluene, catalyst and hydrogen gas as
aforementioned into the generation furnace 1. Further, at the
outside of the inlet nozzle 2, a cylindrical-shaped collision
member 3 was provided. The collision member 3 was set to be able to
interfere in the raw material gas flow introduced from the raw
material supply port 4 located at the lower end of the inlet nozzle
2. In the generation furnace 1 used in this Example, given that the
inner diameter of the inlet nozzle 2, the inner diameter of the
generation furnace 1, the inner diameter of the cylindrical-shaped
collision member 3, the distance from the upper end of the
generation furnace 1 to the raw material mixture gas supply port 4,
the distance from the raw material mixture gas supply port 4 to the
lower end of the collision member 3, and the distance from the raw
material mixture gas supply port 4 to the lower end of the
generation furnace 1 were "a", "b", "c", "d", "e", and "f",
respectively, the ratio among the above dimensions was set as
a:b:c:d:e:f=1.0:3.6:1.8:3.2:2.0:21.0. The raw material gas
supplying rate to the generation furnace was 1850 NL/min., and the
pressure was 1.03 atms.
[0125] The synthesized fibrous structure (intermediate) was baked
at 900.degree. C. in nitrogen gas in order to remove hydrocarbons
such as tar, which had been included as impurities, and thus to
purify. The R value measured by the Raman spectroscopic analysis of
the fibrous structure (intermediate) after receiving the removing
and purification was found to be 0.98.
[0126] Further, the fibrous structure (intermediate) underwent a
high temperature heat treatment at 2600.degree. C. The obtained
aggregates of the precursors underwent pulverization using an air
flow pulverizer in order to produce the precursors which each had
three dimensional network structure and which were substance in the
previous stage of the carbon fibrous structure according to the
present invention. FIG. 3 shows SEM photo of the obtained
precursors as mounted on a sample holder for electron microscope. A
sample for electron microscopes was prepared by dispersing the
obtained precursors into toluene. FIG. 4 show SEM photo of the
sample.
[0127] The result from the examination for distance between the
granular parts of the obtained precursors is shown in Table 1. The
result from the examination for distribution of the particle size
of the granular parts of the obtained precursors is shown in Table
2.
TABLE-US-00001 TABLE 1 Distribution of the length of fine carbon
fibers (pieces) Synthetic Example 1 Synthetic Example 2 <1 .mu.m
2 4 1 .mu.m to <5 .mu.m 58 106 5 .mu.m to <10 .mu.m 57 66 10
.mu.m to <15 .mu.m 45 14 15 .mu.m to <20 .mu.m 21 7 20 .mu.m
to <25 .mu.m 9 2 25 .mu.m to <30 .mu.m 5 0 35 .mu.m to <40
.mu.m 3 1 .gtoreq.40 .mu.m 0 0 Mean length of fine 10.21 .mu.m
10.03 .mu.m carbon fibers
[0128] Further, X-ray diffraction analysis and Raman spectroscopic
analysis were performed on the precursors after the high
temperature heat treatment. The various physical properties of the
precursors obtained in Synthetic Example are shown in FIG. 5.
[0129] It was found that the fibrous structures had an area based
circle-equivalent mean diameter of 70.3 .mu.m. It was also found
that the granular parts in the precursors had the mean particle
size of 0.289 .mu.m, that was 4.8 times larger than the mean outer
diameter of the carbon fibers in the precursors. The mean roundness
of the granular parts was found to be 0.81, and the mean distance
between the granular parts was found to be 10.21 .mu.m.
[0130] Additionally, it was found that precursors had the bulk
density of 0.0042 g/cm.sup.3, Raman I.sub.D/I.sub.G ratio of 0.083,
Raman I.sub.G'/I.sub.G ratio of 0.642, TG combustion temperature of
768.degree. C., spacing of 3.383 angstroms, particle's resistance
of 0.0082 .OMEGA.cm, and density after decompression of 0.20
g/cm.sup.3.
Synthetic Example 2
[0131] By the CVD process, precursors for the carbon fibrous
structures were synthesized using a part of the exhaust gas from
the generation furnace as a recycling gas in order to use as the
carbon source the carbon compounds such as methane, etc., included
in the recycling gas, as well as a fresh toluene.
[0132] The synthesis was carried out in the presence of a mixture
of ferrocene and thiophene as the catalyst, and under the reducing
atmosphere of hydrogen gas. Toluene and the catalyst as a fresh raw
material were heated to 380.degree. C. along with the hydrogen gas
in a preheat furnace, while a part of the exhaust gas taken out
from the lower end of the generation furnace was used as a
recycling gas. After it was adjusted to 380.degree. C., it was
mixed with the fresh raw material gas on the way of the supplying
line for the fresh raw material to the generation furnace. The
mixed gas was then supplied to the generation furnace.
[0133] The composition ratio in the recycling gas used were found
to be CH.sub.4 7.5%, C.sub.6H.sub.6 0.3%, C.sub.2H.sub.2 0.7%,
C.sub.2H.sub.6 0.1%, CO 0.3%, N.sub.2 3.5%, and H.sub.2 87.6% by
the volume based molar ratio. The mixing flow rate was adjusted so
that the mixing molar ratio of methane and benzene in the raw
material gas to be supplied to the generation furnace,
CH.sub.4/C.sub.6H.sub.6 was set to 3.44 (wherein, it was considered
that the toluene in the fresh raw material gas had been decomposed
at 100% to CH.sub.4:C.sub.6H.sub.6 1:1 by the heating in the
preheat furnace).
[0134] In the final raw material gas, C.sub.2H.sub.2,
C.sub.2H.sub.6, and CO which were involved in the recycling gas to
be mixed were naturally included. However, since these ingredients
were very small amount, they may substantially be ignored as the
carbon source.
[0135] Then they were underwent thermal decomposition at
1250.degree. C. in order to obtain the fibrous structures
(intermediate) in an analogous fashion as Synthetic Example 1.
[0136] The constitution of the generation furnace used for the
fibrous structures (intermediate) was the same as that shown in
FIG. 6, except that the cylindrical-shaped collision member 3 was
omitted. The raw material gas supplying rate to the generation
furnace was 1850 NL/min., and the pressure was atms as in the case
of Synthetic Example 1.
[0137] The synthesized fibrous structure (intermediate) was baked
at 900.degree. C. in nitrogen gas in order to remove hydrocarbons
such as tar. The R value measured by the Raman spectroscopic
analysis of the fibrous structure (intermediate) after baking was
found to be 0.83.
[0138] Further, the fibrous structure (intermediate) thus treated
underwent a high temperature heat treatment at 2600.degree. C. The
obtained aggregates of the precursors underwent pulverization using
an air flow pulverizer in order to produce the precursors.
[0139] SEM photo of the obtained precursors as mounted on a sample
holder for electron microscope was in much the same with that of
Synthetic Example 1 shown in FIG. 3. SEM photo of the sample for
electron microscopes prepared by dispersing the obtained precursors
into toluene was also in much the same with that of Synthetic
Example 1 shown in FIG. 4.
[0140] The result from the examination for distance between the
granular parts of the obtained precursors is shown in Table 1. The
result from the examination for distribution of the particle size
of the granular parts of the obtained precursors is shown in Table
2.
TABLE-US-00002 TABLE 2 Distribution of the particle size of
granular parts Synthetic Example 1 Synthetic Example 2 (pieces)
(Precursor) (Precursor) <0.1 .mu.m 0 0 0.1 .mu.m to <0.2
.mu.m 21 10 0.2 .mu.m to <0.3 .mu.m 86 78 0.3 .mu.m to <0.4
.mu.m 52 62 0.4 .mu.m to <0.5 .mu.m 20 24 0.5 .mu.m to <0.6
.mu.m 11 14 0.6 .mu.m to <0.7 .mu.m 5 5 .gtoreq.0.8 .mu.m 5 7
Mean particle size 0.289 .mu.m 0.309 .mu.m of granular parts
[0141] Further, X-ray diffraction analysis and Raman spectroscopic
analysis were performed on the precursors after the high
temperature heat treatment. The various physical properties of the
precursors obtained in Synthetic Example 2 are shown in FIG. 5.
[0142] It was found that the fibrous structures had an area based
circle-equivalent mean diameter of 67.3 .mu.m. It was also found
that the granular parts in the precursors had the mean particle
size of 0.309 .mu.m, that was 5.2 times larger than the mean outer
diameter of the carbon fibers in the precursors. The mean roundness
of the granular parts was found to be 0.78, and the mean distance
between the granular parts was found to be 10.03 .mu.m.
[0143] Additionally, it was found that precursors had the bulk
density of 0.0055 g/cm.sup.3, Raman I.sub.D/I.sub.G ratio of 0.074,
Raman I.sub.G'/I.sub.G ratio of 0.528, TC combustion temperature of
802.degree. C., spacing of 3.386 angstroms, particle's resistance
of 0.0095 .OMEGA.cm, and density after decompression of 0.19
g/cm.sup.3.
Example 1
[0144] To 100 ml of toluene in a lidded vial, the precursors
prepared in Synthetic Example 1 were added at a rate of 30 .mu.g/ml
in order to prepare the dispersion liquid sample of the
precursors.
[0145] To the dispersion liquid sample of the precursors thus
prepared, ultrasonic waves were applied using a ultrasonic cleaner
(manufactured by SND Co., Ltd., Trade Name: USK-3) of which
generated frequency was 38 kHz and power was 150 w, in order to
perform the process of cutting selectively against the
precursors.
[0146] The fine carbon fibrous structures prepared by the above
treatment were observed using an optical microscope and a TEM. From
the result of the observation, it was found that the obtained
carbon fibrous structure possessed a form in which plural number of
fine carbon fibers were extended outwardly from a granular part
which located at the central potion of the structure. Further, from
the observation using TEM, it was also found that most of defects
in the carbon fibrous structure resided at the fine carbon fiber
parts as compared with the number of defects resided at the
granular part. Optical micrographs and TEM photos of the carbon
fibrous structures obtained by the irradiation with the ultrasonic
waves for 500 minutes are shown in FIG. 1A, FIG. 1B, FIG. 1C, FIG.
2A, FIG. 2B, FIG. 2C and FIG. 2D. It was found that the interior of
the fine carbon fiber was hollow (about 5 nm). Further, with
respect to the shape of the outward end portion of the fine carbon
fiber opposite to the granular part, the opened shapes and the
closed shapes in mixed state were observed.
[0147] The distribution of the length of the fine carbon fibers
extended outwardly from the granular part was investigated by
taking a SEM photo of the carbon fibrous structures obtained by the
irradiation with the ultrasonic waves, and then using the image
analysis software, WinRoof.TM. (trade name, marketed by Mitani
Corp.). The result was shown in the Table 3. Further, the result
from the examination for the distribution of the particle size of
the granular parts is shown in Table 4.
[0148] The mean length of the fine carbon fibers in the precursor
of Synthetic Example 1 before the process of cutting selectively
was found to be 10.21 .mu.m, while the mean length of the fine
carbon fibers in the carbon fibrous structure after the ultrasonic
wave irradiation was stated was found to be 4.95 .mu.m, which value
was about half the value of the precursor. This result showed that
many breakages were given in the fine carbon fibers of the
precursors by the process of cutting selectively using the
ultrasonic wave irradiation.
[0149] However, when comparing the mean particle size of the
granular parts of the carbon fibrous structures after 500 minutes'
ultrasonic waves irradiation to that of the granular parts of
precursors, the sizes were found to be about 0.3 .mu.m in both
cases, and thus, no variability was observed in the mean particle
size of the granular parts before and after the ultrasonic wave
irradiation. Considering measurement error, etc., it was found that
the granular parts themselves were hardly destroyed even under the
load condition that many breakages were given in the fine carbon,
and the granular parts still function as the binding site for the
fibers mutually.
[0150] Further, it was found that the granular parts in the carbon
fibrous structures had the mean particle size of 0.304 .mu.m, that
was 5.1 times larger than the mean outer diameter of the carbon
fibers in the carbon fibrous structure. The mean roundness of the
granular parts was found to be 0.84. Therefore, no substantial
change in the physical properties of the granular parts was
observed, when comparing the carbon fibrous structures to the
precursors obtained in Synthetic Example 1 before the cutting
process.
[0151] The measurement results of various physical properties of
the carbon fibrous structure obtained in Example 1 are summarized
in FIG. 5. Further, X-ray diffraction analysis and Raman
spectroscopic analysis were performed on the carbon fibrous
structures in order to investigate the changes in these analyses.
The results are shown in FIG. 7 and FIG. 8, respectively. From the
result of the Raman spectroscopic analysis, a slight increment
trend in the amount of the defects was detected in the data of the
carbon fibrous structure as compared with that of the precursor.
This is due to the existence of the opened shapes' end portions of
the fine carbon fibers in the carbon fibrous structure, wherein the
opened ends are created by the cutting process and they are
recognized as defect portions on this analysis. However, since the
opened end would be created at the position where the defect
existed inherently in the carbon fiber part in the precursor, a
great increment trend in the amount of the defects were not
derived. In the end, a Raman I.sub.D/I.sub.G ratio and a Raman
I.sub.G'/I.sub.G ratio from which high strength and high
electrically conductivity were expected were detected, and thus, it
was shown that the number of defects in the graphene sheets was
low.
[0152] In addition, the G' band showed a almost bilateral symmetry
shape, and thus, it was suggested that the graphene sheets took
cylindrical shapes.
[0153] Furthermore, from the observation in TEM, it was confirmed
that the graphene sheets which constituted the fine carbon fibers
were almost symmetric with respect to the central axis.
[0154] Additionally, it was found that the carbon fibrous
structures after drying had a bulk density of 0.0352 g/cm.sup.3,
Raman I.sub.D/I.sub.G ratio of 0.088, Raman I.sub.G'/I.sub.G ratio
of 0.576, TG combustion temperature of 798.degree. C., spacing of
3.385 angstroms, particle's resistance of 0.0185 .OMEGA.cm, and
density after decompression of 0.17 g/cm.sup.3.
Example 2
[0155] Under the same conditions as in Example 1 except that the
irradiation time of the ultrasonic waves was changed to 1000
minutes, the precursors prepared in Synthetic Example 1 underwent
the process of cutting selectively in order to prepare the carbon
fiber structures. The obtained carbon fiber structures underwent
the same evaluation tests as in Example 1. From the result of the
observation using an optical microscope and a TEM, it was found
that the obtained carbon fibrous structure possessed a form in
which plural number of fine carbon fibers were extended outwardly
from a granular part which located at the central potion of the
structure, as is the case with Example 1.
[0156] The result of the examination for the distribution of the
length of the fine carbon fibers in the obtained carbon fibrous
structures is shown in Table 3, and the result of the examination
for the distribution of the particle size of the granular parts is
shown in Table 4.
[0157] The mean length of the fine carbon fibers in the precursor
of Synthetic Example 1 before the process of cutting selectively
was 10.21 .mu.m, while the mean length of the fine carbon fibers in
the carbon fibrous structure after the ultrasonic wave irradiation
was stated was found to be 5.87 .mu.m, which value was about half
the value of the precursor. This result showed that many breakages
were given in the fine carbon fibers of the precursors by the
process of cutting selectively using the ultrasonic wave
irradiation.
[0158] However, when comparing the mean particle size of the
granular parts of the carbon fibrous structures after 1000 minutes'
ultrasonic waves irradiation to that of the granular parts of
precursors, the sizes were found to be about 0.3 .mu.m in both
cases, and thus, no variability was observed in the mean particle
size of the granular parts before and after the ultrasonic wave
irradiation. Considering measurement error, etc., it was found that
the granular parts themselves were hardly destroyed even under the
load condition that many breakages were given in the fine carbon,
and the granular parts still function as the binding site for the
fibers mutually.
[0159] Optical micrographs and TEM photos of the carbon fibrous
structures obtained in Example 2 are much the same with those of
the carbon fibrous structure obtained in Example 1 which are shown
in FIG. 1A, FIG. 1B, FIG. 1C, FIG. 2A, FIG. 2B, FIG. 2C and FIG.
2D. Thus, it was found that the obtained carbon fibrous structure
possessed a form in which plural number of fine carbon fibers were
extended outwardly from a granular part which located at the
central potion of the structure.
[0160] The measurement results of various physical properties of
the carbon fibrous structure obtained in Example 2 are summarized
in FIG. 5. Although the irradiation time of the ultrasonic waves in
Example 2 was set to be 1000 minutes which was twice as much as 500
minutes in Example 1, this increment in the ultrasonic waves
irradiation time were accompanied by no change in various physical
properties shown in Table 5. Further, X-ray diffraction analysis
and Raman spectroscopic analysis were performed on the carbon
fibrous structures in order to investigate the changes in these
analyses. The results are much the same with the results shown in
FIG. 7 and FIG. 8.
[0161] Further, it was found that the obtained carbon fibrous
structures had a bulk density of 0.0328 g/cm.sup.3, Raman
I.sub.D/I.sub.G ratio of 0.079, Raman I.sub.G'/I.sub.G ratio of
0.614, TG combustion temperature of 781.degree. C., spacing of
3.386 angstroms, particle's resistance of 0.0219 .OMEGA.cm, and
density after decompression of 0.160 g/cm.sup.3.
[0162] Additionally, it was found that the granular parts in the
carbon fibrous structures had the mean particle size of 0.295
.mu.m, that was 4.9 times larger than the mean outer diameter of
the carbon fibers in the carbon fibrous structures. The mean
roundness of the granular parts was found to be 0.82. Therefore, no
substantial change in the physical properties of the granular parts
was observed, when comparing the carbon fibrous structures to the
precursors obtained in Synthetic Example 1 before the cutting
process.
Example 3
[0163] Under the same conditions as in Example 2 except that the
precursors prepared in Synthetic Example 2 were used, the process
of cutting selectively by the ultrasonic waves irradiation for 1000
minutes was performed. The obtained carbon fiber structures
underwent the same evaluation tests as in Example 1. From the
result of the observation using an optical microscope and a TEM, it
was found that the obtained carbon fibrous structure possessed a
form in which plural number of fine carbon fibers were extended
outwardly from a granular part which located at the central potion
of the structure, as is the case with Example 1.
[0164] The result of the examination for the distribution of the
length of the fine carbon fibers in the obtained carbon fibrous
structures is shown in Table 3, and the result of the examination
for the distribution of the particle size of the granular parts is
shown in Table 4.
TABLE-US-00003 TABLE 3 Distribution of Example 1 Example 2 Example
3 the length of (Carbon (Carbon (Carbon fine carbon fibrous fibrous
fibrous fibers (pieces) structure) structure) structure) <1
.mu.m 17 24 7 1 .mu.m to <5 .mu.m 128 104 105 5 .mu.m to <10
.mu.m 29 42 61 10 .mu.m to <15 .mu.m 15 17 19 15 .mu.m to <20
.mu.m 9 8 3 20 .mu.m to <25 .mu.m 1 5 3 25 .mu.m to <30 .mu.m
1 0 2 35 .mu.m to <40 .mu.m 0 0 0 .gtoreq.40 .mu.m 0 0 0 Mean
length of 4.95 .mu.m 5.87 .mu.m 4.20 .mu.m fine carbon fibers
TABLE-US-00004 TABLE 4 Distribution of Example 1 Example 2 Example
3 the particle (Carbon (Carbon (Carbon size of granular fibrous
fibrous fibrous parts (pieces) structure) structure) structure)
<0.1 .mu.m 0 0 0 0.1 .mu.m to <0.2 .mu.m 8 6 20 0.2 .mu.m to
<0.3 .mu.m 85 106 93 0.3 .mu.m to <0.4 .mu.m 75 82 50 0.4
.mu.m to <0.5 .mu.m 19 0 13 0.5 .mu.m to <0.6 .mu.m 2 6 10
0.6 .mu.m to <0.7 .mu.m 4 0 13 .gtoreq.0.8 .mu.m 7 0 1 Mean
particle 0.304 .mu.m 0.295 .mu.m 0.296 .mu.m size of granular
parts
[0165] The mean length of the fine carbon fibers in the precursor
of Synthetic Example 2 before the process of cutting selectively
was found to be 10.03 .mu.m, while the mean length of the fine
carbon fibers in the carbon fibrous structure after the ultrasonic
wave irradiation was stated was found to be 4.20 .mu.m, which value
was about half the value of the precursor. This result showed that
many breakages were given in the fine carbon fibers of the
precursors by the process of cutting selectively using the
ultrasonic wave irradiation.
[0166] However, when comparing the mean particle size of the
granular parts of the carbon fibrous structures after 1000 minutes'
ultrasonic waves irradiation to that of the granular parts of
precursors, the sizes were found to be about 0.3 .mu.m in both
cases, and thus, no variability was observed in the mean particle
size of the granular parts before and after the ultrasonic wave
irradiation. Considering measurement error, etc., it was found that
the granular parts themselves were hardly destroyed even under the
load condition that many breakages were given in the fine carbon,
and the granular parts still function as the binding site for the
fibers mutually.
[0167] Optical micrographs and TEM photos of the carbon fibrous
structures obtained in Example 3 are much the same with those of
the carbon fibrous structure obtained in Example 1 which are shown
in FIG. 1A, FIG. 1B, FIG. 1C, FIG. 2A, FIG. 2B, FIG. 2C and FIG.
2D. Thus, it was found that the obtained carbon fibrous structure
possessed a form in which plural number of fine carbon fibers were
extended outwardly from a granular part which located at the
central potion of the structure. Further, X-ray diffraction
analysis and Raman spectroscopic analysis were performed on the
carbon fibrous structures in order to investigate the changes in
these analyses. The results are much the same with the results
shown in FIG. 7 and FIG. 8.
[0168] The measurement results of various physical properties of
the carbon fibrous structure obtained in Example 3 are summarized
in FIG. 5.
TABLE-US-00005 TABLE 5 Example 1 Example 2 Example 3 Synthetic
Synthetic (Carbon (Carbon (Carbon Example 1 Example 2 fibrous
fibrous fibrous Items (Precursor) (Precursor) structure) structure)
structure) Area based circle-equivalent 70.3 67.3 -- -- -- mean
diameter (.mu.m) Mean particle size of granular 0.289 0.309 0.304
0.295 0.296 parts (.mu.m) Mean roundness of granular 0.81 0.78 0.84
0.82 0.80 parts Mean length of fine carbon 10.21 10.03 -- -- --
fibers in precursor (.mu.m) Mean length of fine carbon -- -- 4.95
5.87 4.2 fibers in carbon fibrous structure Ratio of mean particle
4.8 5.2 5.1 4.9 4.9 diameter of granular parts and mean diameter of
fine carbon fibers Bulk density (g/cm.sup.3) 0.0042 0.0055 0.0352
0.0328 0.0382 I.sub.D/I.sub.G ratio 0.083 0.074 0.088 0.079 0.091
I.sub.G'/I.sub.G ratio 0.642 0.528 0.576 0.614 0.544 TG combustion
temperature (.degree. C.) 768 802 798 781 775 Spacing for (002)
faces (.ANG.) 3.383 3.386 3.385 3.386 3.388 Particle's resistance
at 0.5 0.0172 0.0193 0.0682 0.0734 0.1473 g/cm.sup.3 (.OMEGA. cm)
Particle's resistance at 0.8 0.0094 0.0109 0.0229 0.0276 0.0468
g/cm.sup.3 (.OMEGA. cm) Particle's resistance at 0.9 0.0082 0.0095
0.0185 0.0219 0.0369 g/cm.sup.3 (.OMEGA. cm) Density after
decompression 0.2 0.190 0.170 0.160 0.190 (g/cm.sup.3)
[0169] Further, it was found that the obtained carbon fibrous
structures had a bulk density of 0.0382 g/cm.sup.3, Raman
I.sub.D/I.sub.G ratio of 0.091, Raman I.sub.G'/I.sub.G ratio of
0.544, TG combustion temperature of 775.degree. C., spacing of
3.388 angstroms, particle's resistance of 0.0369 .OMEGA.cm, and
density after decompression of 0.190 g/cm.sup.3.
[0170] Additionally, it was found that the granular parts in the
carbon fibrous structures had the mean particle size of 0.296
.mu.m, that was 4.9 times larger than the mean outer diameter of
the carbon fibers in the carbon fibrous structures. The mean
roundness of the granular parts was found to be 0.80. Therefore, no
substantial change in the physical properties of the granular parts
was observed, when comparing the carbon fibrous structures to the
precursors obtained in Synthetic Example 2 before the cutting
process.
Examples 4-6
[0171] To 100 parts by weight of polyurethane resin solution
(non-volatile moiety: 20%), the carbon fibrous structures obtained
in Example 1 were added at respective ratios shown in Table 6. As
results, the coating compositions where the carbon fibrous
structures were dispersed in the polyurethane resin solution were
prepared.
[0172] Coating compositions thus obtained were developed
individually on a glass plate in order to obtain hardened coated
films of respective thicknesses shown in Table 6. The hardened
films were tested for total light transmittance, and surface
resistivity. The obtained results are shown in Table 6.
Incidentally, the coating abilities of the coating compositions
were good and the compositions can be coated by a bar coater with
ease.
TABLE-US-00006 TABLE 6 Example Example Example Control Control 4 5
6 1 2 Polyurethane 100 100 100 100 100 resin Carbon 5 2 5 -- --
fibrous structure multi-layered -- -- -- 1.5 5 carbon nanotube Film
0.2 1 1.5 1 1 thickness (.mu.m) Total light 88.2 87.3 71.7 22.7
N.D. transmittance (%) Surface 3.8 .times. 10.sup.8 3.6 .times.
10.sup.8 4.9 .times. 10.sup.8 >10.sup.12 >10.sup.12
resistivity (.OMEGA./cm.sup.2)
Example 7
[0173] in order to observe the presence and dispersion condition of
the carbon fibrous structures in the matrix, a polyurethane coated
film (about 500 nm in thickness) were formed so that the film
contained the carbon fibrous structures obtained in Example 1 at a
ratio of 0.2% by weight based on the total weight.
[0174] Optical micrograph of the coated film is shown in FIG. 9. It
is apparent from FIG. 9 that the carbon fibrous structure showed a
good dispersibility in the resin matrix.
(Controls 1 and 2)
[0175] To 100 parts by weight of polyurethane resin solution
(non-volatile moiety: 20%), multilayered carbon nanotubes
(manufactured by Tsinghua-Nafine, outside diameter: 10-20 nm,
length: several micrometers to several ten micrometers) was added
at respective ratios shown in Table 6. As results, the coating
compositions where the multilayered carbon nanotubes were dispersed
in the polyurethane resin solution were prepared.
[0176] Coating compositions thus obtained were developed
individually on a glass plate in order to obtain hardened coated
films of respective thicknesses shown in Table 6. The hardened
films were tested for total light transmittance, and surface
resistivity. The obtained results are shown in Table 6.
Incidentally, the coating abilities of the coating compositions
were good and the compositions can be coated by a bar coater with
ease.
* * * * *